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Linux/mm/mremap.c

  1 /*
  2  *      mm/mremap.c
  3  *
  4  *      (C) Copyright 1996 Linus Torvalds
  5  *
  6  *      Address space accounting code   <alan@lxorguk.ukuu.org.uk>
  7  *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
  8  */
  9 
 10 #include <linux/mm.h>
 11 #include <linux/hugetlb.h>
 12 #include <linux/shm.h>
 13 #include <linux/ksm.h>
 14 #include <linux/mman.h>
 15 #include <linux/swap.h>
 16 #include <linux/capability.h>
 17 #include <linux/fs.h>
 18 #include <linux/swapops.h>
 19 #include <linux/highmem.h>
 20 #include <linux/security.h>
 21 #include <linux/syscalls.h>
 22 #include <linux/mmu_notifier.h>
 23 #include <linux/uaccess.h>
 24 #include <linux/mm-arch-hooks.h>
 25 
 26 #include <asm/cacheflush.h>
 27 #include <asm/tlbflush.h>
 28 
 29 #include "internal.h"
 30 
 31 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
 32 {
 33         pgd_t *pgd;
 34         pud_t *pud;
 35         pmd_t *pmd;
 36 
 37         pgd = pgd_offset(mm, addr);
 38         if (pgd_none_or_clear_bad(pgd))
 39                 return NULL;
 40 
 41         pud = pud_offset(pgd, addr);
 42         if (pud_none_or_clear_bad(pud))
 43                 return NULL;
 44 
 45         pmd = pmd_offset(pud, addr);
 46         if (pmd_none(*pmd))
 47                 return NULL;
 48 
 49         return pmd;
 50 }
 51 
 52 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
 53                             unsigned long addr)
 54 {
 55         pgd_t *pgd;
 56         pud_t *pud;
 57         pmd_t *pmd;
 58 
 59         pgd = pgd_offset(mm, addr);
 60         pud = pud_alloc(mm, pgd, addr);
 61         if (!pud)
 62                 return NULL;
 63 
 64         pmd = pmd_alloc(mm, pud, addr);
 65         if (!pmd)
 66                 return NULL;
 67 
 68         VM_BUG_ON(pmd_trans_huge(*pmd));
 69 
 70         return pmd;
 71 }
 72 
 73 static void take_rmap_locks(struct vm_area_struct *vma)
 74 {
 75         if (vma->vm_file)
 76                 i_mmap_lock_write(vma->vm_file->f_mapping);
 77         if (vma->anon_vma)
 78                 anon_vma_lock_write(vma->anon_vma);
 79 }
 80 
 81 static void drop_rmap_locks(struct vm_area_struct *vma)
 82 {
 83         if (vma->anon_vma)
 84                 anon_vma_unlock_write(vma->anon_vma);
 85         if (vma->vm_file)
 86                 i_mmap_unlock_write(vma->vm_file->f_mapping);
 87 }
 88 
 89 static pte_t move_soft_dirty_pte(pte_t pte)
 90 {
 91         /*
 92          * Set soft dirty bit so we can notice
 93          * in userspace the ptes were moved.
 94          */
 95 #ifdef CONFIG_MEM_SOFT_DIRTY
 96         if (pte_present(pte))
 97                 pte = pte_mksoft_dirty(pte);
 98         else if (is_swap_pte(pte))
 99                 pte = pte_swp_mksoft_dirty(pte);
100 #endif
101         return pte;
102 }
103 
104 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
105                 unsigned long old_addr, unsigned long old_end,
106                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
107                 unsigned long new_addr, bool need_rmap_locks, bool *need_flush)
108 {
109         struct mm_struct *mm = vma->vm_mm;
110         pte_t *old_pte, *new_pte, pte;
111         spinlock_t *old_ptl, *new_ptl;
112         bool force_flush = false;
113         unsigned long len = old_end - old_addr;
114 
115         /*
116          * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
117          * locks to ensure that rmap will always observe either the old or the
118          * new ptes. This is the easiest way to avoid races with
119          * truncate_pagecache(), page migration, etc...
120          *
121          * When need_rmap_locks is false, we use other ways to avoid
122          * such races:
123          *
124          * - During exec() shift_arg_pages(), we use a specially tagged vma
125          *   which rmap call sites look for using is_vma_temporary_stack().
126          *
127          * - During mremap(), new_vma is often known to be placed after vma
128          *   in rmap traversal order. This ensures rmap will always observe
129          *   either the old pte, or the new pte, or both (the page table locks
130          *   serialize access to individual ptes, but only rmap traversal
131          *   order guarantees that we won't miss both the old and new ptes).
132          */
133         if (need_rmap_locks)
134                 take_rmap_locks(vma);
135 
136         /*
137          * We don't have to worry about the ordering of src and dst
138          * pte locks because exclusive mmap_sem prevents deadlock.
139          */
140         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
141         new_pte = pte_offset_map(new_pmd, new_addr);
142         new_ptl = pte_lockptr(mm, new_pmd);
143         if (new_ptl != old_ptl)
144                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
145         arch_enter_lazy_mmu_mode();
146 
147         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
148                                    new_pte++, new_addr += PAGE_SIZE) {
149                 if (pte_none(*old_pte))
150                         continue;
151 
152                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
153                 /*
154                  * If we are remapping a dirty PTE, make sure
155                  * to flush TLB before we drop the PTL for the
156                  * old PTE or we may race with page_mkclean().
157                  *
158                  * This check has to be done after we removed the
159                  * old PTE from page tables or another thread may
160                  * dirty it after the check and before the removal.
161                  */
162                 if (pte_present(pte) && pte_dirty(pte))
163                         force_flush = true;
164                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
165                 pte = move_soft_dirty_pte(pte);
166                 set_pte_at(mm, new_addr, new_pte, pte);
167         }
168 
169         arch_leave_lazy_mmu_mode();
170         if (new_ptl != old_ptl)
171                 spin_unlock(new_ptl);
172         pte_unmap(new_pte - 1);
173         if (force_flush)
174                 flush_tlb_range(vma, old_end - len, old_end);
175         else
176                 *need_flush = true;
177         pte_unmap_unlock(old_pte - 1, old_ptl);
178         if (need_rmap_locks)
179                 drop_rmap_locks(vma);
180 }
181 
182 #define LATENCY_LIMIT   (64 * PAGE_SIZE)
183 
184 unsigned long move_page_tables(struct vm_area_struct *vma,
185                 unsigned long old_addr, struct vm_area_struct *new_vma,
186                 unsigned long new_addr, unsigned long len,
187                 bool need_rmap_locks)
188 {
189         unsigned long extent, next, old_end;
190         pmd_t *old_pmd, *new_pmd;
191         bool need_flush = false;
192         unsigned long mmun_start;       /* For mmu_notifiers */
193         unsigned long mmun_end;         /* For mmu_notifiers */
194 
195         old_end = old_addr + len;
196         flush_cache_range(vma, old_addr, old_end);
197 
198         mmun_start = old_addr;
199         mmun_end   = old_end;
200         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
201 
202         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
203                 cond_resched();
204                 next = (old_addr + PMD_SIZE) & PMD_MASK;
205                 /* even if next overflowed, extent below will be ok */
206                 extent = next - old_addr;
207                 if (extent > old_end - old_addr)
208                         extent = old_end - old_addr;
209                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
210                 if (!old_pmd)
211                         continue;
212                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
213                 if (!new_pmd)
214                         break;
215                 if (pmd_trans_huge(*old_pmd)) {
216                         if (extent == HPAGE_PMD_SIZE) {
217                                 bool moved;
218                                 /* See comment in move_ptes() */
219                                 if (need_rmap_locks)
220                                         take_rmap_locks(vma);
221                                 moved = move_huge_pmd(vma, old_addr, new_addr,
222                                                     old_end, old_pmd, new_pmd,
223                                                     &need_flush);
224                                 if (need_rmap_locks)
225                                         drop_rmap_locks(vma);
226                                 if (moved)
227                                         continue;
228                         }
229                         split_huge_pmd(vma, old_pmd, old_addr);
230                         if (pmd_trans_unstable(old_pmd))
231                                 continue;
232                 }
233                 if (pte_alloc(new_vma->vm_mm, new_pmd, new_addr))
234                         break;
235                 next = (new_addr + PMD_SIZE) & PMD_MASK;
236                 if (extent > next - new_addr)
237                         extent = next - new_addr;
238                 if (extent > LATENCY_LIMIT)
239                         extent = LATENCY_LIMIT;
240                 move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
241                           new_pmd, new_addr, need_rmap_locks, &need_flush);
242         }
243         if (need_flush)
244                 flush_tlb_range(vma, old_end-len, old_addr);
245 
246         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
247 
248         return len + old_addr - old_end;        /* how much done */
249 }
250 
251 static unsigned long move_vma(struct vm_area_struct *vma,
252                 unsigned long old_addr, unsigned long old_len,
253                 unsigned long new_len, unsigned long new_addr, bool *locked)
254 {
255         struct mm_struct *mm = vma->vm_mm;
256         struct vm_area_struct *new_vma;
257         unsigned long vm_flags = vma->vm_flags;
258         unsigned long new_pgoff;
259         unsigned long moved_len;
260         unsigned long excess = 0;
261         unsigned long hiwater_vm;
262         int split = 0;
263         int err;
264         bool need_rmap_locks;
265 
266         /*
267          * We'd prefer to avoid failure later on in do_munmap:
268          * which may split one vma into three before unmapping.
269          */
270         if (mm->map_count >= sysctl_max_map_count - 3)
271                 return -ENOMEM;
272 
273         /*
274          * Advise KSM to break any KSM pages in the area to be moved:
275          * it would be confusing if they were to turn up at the new
276          * location, where they happen to coincide with different KSM
277          * pages recently unmapped.  But leave vma->vm_flags as it was,
278          * so KSM can come around to merge on vma and new_vma afterwards.
279          */
280         err = ksm_madvise(vma, old_addr, old_addr + old_len,
281                                                 MADV_UNMERGEABLE, &vm_flags);
282         if (err)
283                 return err;
284 
285         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
286         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
287                            &need_rmap_locks);
288         if (!new_vma)
289                 return -ENOMEM;
290 
291         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
292                                      need_rmap_locks);
293         if (moved_len < old_len) {
294                 err = -ENOMEM;
295         } else if (vma->vm_ops && vma->vm_ops->mremap) {
296                 err = vma->vm_ops->mremap(new_vma);
297         }
298 
299         if (unlikely(err)) {
300                 /*
301                  * On error, move entries back from new area to old,
302                  * which will succeed since page tables still there,
303                  * and then proceed to unmap new area instead of old.
304                  */
305                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
306                                  true);
307                 vma = new_vma;
308                 old_len = new_len;
309                 old_addr = new_addr;
310                 new_addr = err;
311         } else {
312                 arch_remap(mm, old_addr, old_addr + old_len,
313                            new_addr, new_addr + new_len);
314         }
315 
316         /* Conceal VM_ACCOUNT so old reservation is not undone */
317         if (vm_flags & VM_ACCOUNT) {
318                 vma->vm_flags &= ~VM_ACCOUNT;
319                 excess = vma->vm_end - vma->vm_start - old_len;
320                 if (old_addr > vma->vm_start &&
321                     old_addr + old_len < vma->vm_end)
322                         split = 1;
323         }
324 
325         /*
326          * If we failed to move page tables we still do total_vm increment
327          * since do_munmap() will decrement it by old_len == new_len.
328          *
329          * Since total_vm is about to be raised artificially high for a
330          * moment, we need to restore high watermark afterwards: if stats
331          * are taken meanwhile, total_vm and hiwater_vm appear too high.
332          * If this were a serious issue, we'd add a flag to do_munmap().
333          */
334         hiwater_vm = mm->hiwater_vm;
335         vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
336 
337         /* Tell pfnmap has moved from this vma */
338         if (unlikely(vma->vm_flags & VM_PFNMAP))
339                 untrack_pfn_moved(vma);
340 
341         if (do_munmap(mm, old_addr, old_len) < 0) {
342                 /* OOM: unable to split vma, just get accounts right */
343                 vm_unacct_memory(excess >> PAGE_SHIFT);
344                 excess = 0;
345         }
346         mm->hiwater_vm = hiwater_vm;
347 
348         /* Restore VM_ACCOUNT if one or two pieces of vma left */
349         if (excess) {
350                 vma->vm_flags |= VM_ACCOUNT;
351                 if (split)
352                         vma->vm_next->vm_flags |= VM_ACCOUNT;
353         }
354 
355         if (vm_flags & VM_LOCKED) {
356                 mm->locked_vm += new_len >> PAGE_SHIFT;
357                 *locked = true;
358         }
359 
360         return new_addr;
361 }
362 
363 static struct vm_area_struct *vma_to_resize(unsigned long addr,
364         unsigned long old_len, unsigned long new_len, unsigned long *p)
365 {
366         struct mm_struct *mm = current->mm;
367         struct vm_area_struct *vma = find_vma(mm, addr);
368         unsigned long pgoff;
369 
370         if (!vma || vma->vm_start > addr)
371                 return ERR_PTR(-EFAULT);
372 
373         if (is_vm_hugetlb_page(vma))
374                 return ERR_PTR(-EINVAL);
375 
376         /* We can't remap across vm area boundaries */
377         if (old_len > vma->vm_end - addr)
378                 return ERR_PTR(-EFAULT);
379 
380         if (new_len == old_len)
381                 return vma;
382 
383         /* Need to be careful about a growing mapping */
384         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
385         pgoff += vma->vm_pgoff;
386         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
387                 return ERR_PTR(-EINVAL);
388 
389         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
390                 return ERR_PTR(-EFAULT);
391 
392         if (vma->vm_flags & VM_LOCKED) {
393                 unsigned long locked, lock_limit;
394                 locked = mm->locked_vm << PAGE_SHIFT;
395                 lock_limit = rlimit(RLIMIT_MEMLOCK);
396                 locked += new_len - old_len;
397                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
398                         return ERR_PTR(-EAGAIN);
399         }
400 
401         if (!may_expand_vm(mm, vma->vm_flags,
402                                 (new_len - old_len) >> PAGE_SHIFT))
403                 return ERR_PTR(-ENOMEM);
404 
405         if (vma->vm_flags & VM_ACCOUNT) {
406                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
407                 if (security_vm_enough_memory_mm(mm, charged))
408                         return ERR_PTR(-ENOMEM);
409                 *p = charged;
410         }
411 
412         return vma;
413 }
414 
415 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
416                 unsigned long new_addr, unsigned long new_len, bool *locked)
417 {
418         struct mm_struct *mm = current->mm;
419         struct vm_area_struct *vma;
420         unsigned long ret = -EINVAL;
421         unsigned long charged = 0;
422         unsigned long map_flags;
423 
424         if (offset_in_page(new_addr))
425                 goto out;
426 
427         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
428                 goto out;
429 
430         /* Ensure the old/new locations do not overlap */
431         if (addr + old_len > new_addr && new_addr + new_len > addr)
432                 goto out;
433 
434         ret = do_munmap(mm, new_addr, new_len);
435         if (ret)
436                 goto out;
437 
438         if (old_len >= new_len) {
439                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
440                 if (ret && old_len != new_len)
441                         goto out;
442                 old_len = new_len;
443         }
444 
445         vma = vma_to_resize(addr, old_len, new_len, &charged);
446         if (IS_ERR(vma)) {
447                 ret = PTR_ERR(vma);
448                 goto out;
449         }
450 
451         map_flags = MAP_FIXED;
452         if (vma->vm_flags & VM_MAYSHARE)
453                 map_flags |= MAP_SHARED;
454 
455         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
456                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
457                                 map_flags);
458         if (offset_in_page(ret))
459                 goto out1;
460 
461         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
462         if (!(offset_in_page(ret)))
463                 goto out;
464 out1:
465         vm_unacct_memory(charged);
466 
467 out:
468         return ret;
469 }
470 
471 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
472 {
473         unsigned long end = vma->vm_end + delta;
474         if (end < vma->vm_end) /* overflow */
475                 return 0;
476         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
477                 return 0;
478         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
479                               0, MAP_FIXED) & ~PAGE_MASK)
480                 return 0;
481         return 1;
482 }
483 
484 /*
485  * Expand (or shrink) an existing mapping, potentially moving it at the
486  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
487  *
488  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
489  * This option implies MREMAP_MAYMOVE.
490  */
491 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
492                 unsigned long, new_len, unsigned long, flags,
493                 unsigned long, new_addr)
494 {
495         struct mm_struct *mm = current->mm;
496         struct vm_area_struct *vma;
497         unsigned long ret = -EINVAL;
498         unsigned long charged = 0;
499         bool locked = false;
500 
501         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
502                 return ret;
503 
504         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
505                 return ret;
506 
507         if (offset_in_page(addr))
508                 return ret;
509 
510         old_len = PAGE_ALIGN(old_len);
511         new_len = PAGE_ALIGN(new_len);
512 
513         /*
514          * We allow a zero old-len as a special case
515          * for DOS-emu "duplicate shm area" thing. But
516          * a zero new-len is nonsensical.
517          */
518         if (!new_len)
519                 return ret;
520 
521         if (down_write_killable(&current->mm->mmap_sem))
522                 return -EINTR;
523 
524         if (flags & MREMAP_FIXED) {
525                 ret = mremap_to(addr, old_len, new_addr, new_len,
526                                 &locked);
527                 goto out;
528         }
529 
530         /*
531          * Always allow a shrinking remap: that just unmaps
532          * the unnecessary pages..
533          * do_munmap does all the needed commit accounting
534          */
535         if (old_len >= new_len) {
536                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
537                 if (ret && old_len != new_len)
538                         goto out;
539                 ret = addr;
540                 goto out;
541         }
542 
543         /*
544          * Ok, we need to grow..
545          */
546         vma = vma_to_resize(addr, old_len, new_len, &charged);
547         if (IS_ERR(vma)) {
548                 ret = PTR_ERR(vma);
549                 goto out;
550         }
551 
552         /* old_len exactly to the end of the area..
553          */
554         if (old_len == vma->vm_end - addr) {
555                 /* can we just expand the current mapping? */
556                 if (vma_expandable(vma, new_len - old_len)) {
557                         int pages = (new_len - old_len) >> PAGE_SHIFT;
558 
559                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
560                                        vma->vm_pgoff, NULL)) {
561                                 ret = -ENOMEM;
562                                 goto out;
563                         }
564 
565                         vm_stat_account(mm, vma->vm_flags, pages);
566                         if (vma->vm_flags & VM_LOCKED) {
567                                 mm->locked_vm += pages;
568                                 locked = true;
569                                 new_addr = addr;
570                         }
571                         ret = addr;
572                         goto out;
573                 }
574         }
575 
576         /*
577          * We weren't able to just expand or shrink the area,
578          * we need to create a new one and move it..
579          */
580         ret = -ENOMEM;
581         if (flags & MREMAP_MAYMOVE) {
582                 unsigned long map_flags = 0;
583                 if (vma->vm_flags & VM_MAYSHARE)
584                         map_flags |= MAP_SHARED;
585 
586                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
587                                         vma->vm_pgoff +
588                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
589                                         map_flags);
590                 if (offset_in_page(new_addr)) {
591                         ret = new_addr;
592                         goto out;
593                 }
594 
595                 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
596         }
597 out:
598         if (offset_in_page(ret)) {
599                 vm_unacct_memory(charged);
600                 locked = 0;
601         }
602         up_write(&current->mm->mmap_sem);
603         if (locked && new_len > old_len)
604                 mm_populate(new_addr + old_len, new_len - old_len);
605         return ret;
606 }
607 

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